The disclosure relates to a solenoid valve having a magnet armature, which is operatively connected to a sealing element of the solenoid valve in order to move the latter, and having an armature opposing piece which is arranged at the end of the magnet armature.
Solenoid valves of the type mentioned at the beginning are known from the prior art. They are usually used for driver assistant devices, in particular ABS, TCS or ESP devices. The solenoid valve has the magnet armature which is arranged so as to be movable, in particular axially, in the solenoid valve. The magnet armature is operatively connected to the sealing element of the solenoid valve with the result that when the magnet armature moves, the sealing element is also moved. The sealing element is usually provided for closing or clearing a valve opening of the solenoid valve. If the sealing element is arranged with the purpose of closing the valve opening, it is usually seated in a valve seat of the solenoid valve, which valve seat is assigned both to the valve opening and to the sealing element. For example, the sealing element is inserted into a recess in the magnet armature and held therein, wherein the recess is preferably provided on an end side, facing away from the armature opposing piece, of the magnet armature.
In addition to the magnet armature, the solenoid valve also has the armature opposing piece which is embodied, for example, as a pole core. The pole core is usually held in a positionally fixed fashion with respect to a housing of the solenoid valve, while the magnet armature can be moved with respect to the housing. In order to bring about this movement, the magnet armature and the armature opposing piece interact. In this context, the armature opposing piece has, for example, one or more coils, while the magnet armature is composed of a magnetizable or magnetic material. The armature opposing piece is provided at the end of the magnet armature. The magnet armature and the armature opposing piece are usually arranged with respect to one another in such a way that they cannot enter into connection with one another, irrespective of the movement of the magnet armature. Accordingly, a gap, referred to as the air gap or the working air gap, is present between the magnet armature and the armature opposing piece or between the end side, facing the armature opposing piece, of the magnet armature and the end side, facing the magnet armature, of the armature opposing piece. The size of the air gap is dependent on the position of the magnet armature with respect to the armature opposing piece. The size of the air gap accordingly changes when the magnet armature moves.
The magnet armature and the armature opposing piece together form an actuating device. The magnetic force which can be generated by this actuating device, and which is implemented by the movement of the magnet armature, is characterized by the size of the working air gap. This means that the magnetic force is dependent on the size of the working air gap, wherein the magnetic force increases very strongly—usually exponentially—when the working air gap becomes smaller. This strong increase in a working air gap which is becoming smaller makes the continuous adjustability or the proportionalization of the solenoid valve more difficult.
It is generally known that the strong increase in the magnetic force can be eliminated or at least reduced by means of what is referred to as a plunger stage. In order to implement the plunger stage, an area of the armature opposing piece engages at least in certain areas in a recess in the magnet armature as soon as the magnet armature undershoots a specific distance from the armature opposing piece. However, the implementation of such a plunger stage in a solenoid valve is costly because very precise guidance of the magnet armature with respect to the armature opposing piece is necessary in order to avoid the magnet armature and armature opposing piece impacting against one another or contacting one another, also in the region of the plunger stage. Such impacting or contact would significantly compromise the efficiency level of the actuating device which is composed of the magnet armature and armature opposing element.
Precise guidance can be formed, for example, by precise fitting of the magnet armature into a magnet armature guide, for example of a housing of the solenoid valve. On the other hand, the magnet armature must, however, also be capable of being moved as easily as possible, that is to say without a large application of force. Therefore, very small tolerances have to be implemented during the manufacture of the solenoid valve in order, on the one hand, to make the plunger stage possible and, on the other hand, to permit easy movement of the solenoid valve. However, this results in high manufacturing costs.